The present invention relates to a system for controlling the ignition timing of an internal combustion engine having a turbocharger, and more particularly to a system for controlling the ignition timing at cold engine operation.
In the engine having a turbocharger, the pressure of intake air greatly increases during supercharging operation, which results in an increase of the pressure of mixture compressed in cylinders. Such a high pressure is apt to induce "knocking" in the engine.
Japanese patent laid open 56-99066 discloses a system for preventing the knocking. The system is adapted to control the ignition timing in the retard direction during supercharging operation and to control the timing in the advance direction at non-supercharging operation. However, the knocking does not occur at cold engine operation or at low temperature of intake air, since the detonation causing the knocking occurs under conditions of high compression pressure at high temperature in cylinders. In the system of the prior art, ignition timing is retarded also in such a cold engine condition that knocking hardly occur, which decreases operability of the engine.